In the process of manufacturing semiconductor wafers or LCDs ("workpieces" hereinafter), the workpieces are normally subject to many wet cleaning steps using chemicals. The chemicals are rinsed away using deionized water after the cleansing step. If the workpiece is allowed to dry naturally, the water can leave some stains or spots on the surface of the workpiece, which may result in a defective product. Thus, various dryer systems have been developed to dry the surface of the workpiece throughly, so as not to leave any residue thereon.
For drying workpieces after the rinsing step, a rotary drying apparatus utilizing centrifugal force were used. However, this type of dryer does not show satisfactory drying performance, and the rate of defective product gets higher as the capacity of a semiconductor memory and the size of a LCD substrate increase.
Thus, new dryer systems using alcohol vapor (typically called as alcohol vapor dryer systems) have been developed and used widely in order to solve the above mentioned problems. In the vapor dryer system, alcohol (e.g IPA) condenses and combines with the remaining water droplets on the surface of the workpiece. By this combination, the water droplet loses its surface tension and is released from the surface of the workpiece to be discharged.
Many conventional dryer systems employ only one chamber, and both alcohol vaporization and drying process are carried out within the chamber. For example, liquid IPA is supplied to the bottom of the chamber and heated to a temperature around 240.degree. C., which is three times higher than the boiling point of liquid IPA. Then the workpiece to be dried is exposed to the IPA vapor cloud generated by the heating process in the same chamber. This type of vapor dryer systems are disclosed by Bettcher in U.S. Pat. No. 4,841,645, and many other publications.
However, those conventional vapor dryer systems retain several drawbacks. Since the operation of carrying in/out of the workpiece to/from a dryer system is performed in the very chamber where the liquid IPA is heated and vaporized, the chamber cannot be sealed. Thus, combined with the fact that the liquid IPA is heated at a very high temperature to produce and transfer the IPA vapor, there are substantial chances of fire due to IPA leakage. Further, the rate of producing defective product may increase since the workpiece is in contact with the various contaminants in the air, which was introduced into the chamber whenever workpiece is carried into/out of the chamber.
In addition, because there is no separate control means for controlling the volume of the supplied IPA vapor in the conventional vapor dryer systems, the operating conditions for the drying process should be maintained as initially set. Therefore it is impossible to adjust the volume of the IPA vapor according to the size of the workpiece to be dried. Thus, the workpiece cannot be dried throughly when the workpiece is relatively large, and excess IPA vapors are supplied when the workpiece is relatively small, which will lead to an increased defective rate or increased cost, respectively.
A dryer system which partly addresses the above described problems is disclosed by Robert S. in U.S. Pat. No. 5,226,242 which was assigned to Santa Clara Plastics. In the system disclosed by Robert, an area for generating the IPA vapor and an area for drying the workpiece are separated. In this system, two vessels are disposed one inside the other such that a vapor generating region is formed in the space between the two vessels. Vapor generation takes place in the space between the bottom walls of the two vessels, and a base heater plate along the bottom wall of the outer vessel provides the heat required to vaporize the liquid IPA. Heated nitrogen gas is also provided to the vapor generation area to assist in the efficient generation of vapors. Thus generated vapor and the nitrogen then flow into the space between the two vessels above the region in which the vapor is generated, and then flow into the inner vessel for drying the workpiece deposited therein.
However, in the alcohol vapor dryer system disclosed by Robert, it is impossible to generate the IPA vapor in advance in the vapor generated area before the actual drying process begins. This is due to the fact that, if the IPA vapor is generated in advance, it will flow into the inner vessel through the injection channels between the two vessels before the drying process starts. Thus, the IPA vapor is generated and is supplied to the inner vessel (which corresponds to a process chamber) right after the process actually begins. With this configuration, it will take a considerable amount of time for the IPA vapor to reach the surface of the workpiece which has been already introduced in the inner vessel. This may allow some water droplets on the surface of the workpiece to be dried naturally in the mean time, by the heat of the inner vessel itself (though the actual size of the droplet varies, typically it is small enough to be dried easily by a small quantity of heat). As mentioned above, the natural dry of the workpiece is likely to leave water residue spots on the surface of the workpiece, which will eventually increase the defective rate of the final products. Further, the system is not completely free from the risk of fire.
Accordingly, it is an object of the present invention to solve the above mentioned drawbacks of the conventional dryer system and to provide a vapor dryer system which enables to completely separate the chamber where the workpiece are dried from the vapor generating region.
Another object of the present invention is to provide an alcohol vapor dryer system which is completely free from the chances of fire.
Further another object of the present invention is to provide an alcohol vapor dryer system which allows the operator to adjust the conditions for drying process easily, according to the size of the workpiece and the shape of the jig that holds the workpiece during the entire drying process.
It is also an object of the present invention to provide an alcohol vapor dryer system which can prevent any part of the workpiece from being dried naturally.
It is still a further object of the present invention to provide an IPA vapor dryer that performs its drying process with optimal condition, by modifying the configuration of the spraying pipes which spray the IPA vapor and the heated nitrogen gas toward the workpiece, and by adjusting the spraying angle of the through holes (i.e. jets) formed on the spraying pipes, according to the size of the workpiece and the shape of the jig holding the workpiece during the drying process.